Piston having oval shaped crown

ABSTRACT

A piston for connection by a piston pin and connecting rod to a crankshaft for reciprocating in a cylinder of an internal combustion engine. The piston has a crown and top land region, an intermediate region including at least one additional land, and a skirt region. Cross sections through the crown and top land region transverse to the cylinder axis are ovals whose major axes are generally parallel to the longitudinal axis of the piston pin. Cross sections through the intermediate region are either circular or oval, major axes of each of the ovals being generally transverse to the longitudinal axis of the piston pin.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a novel configuration for a piston for afour-stroke cycle internal combustion engine.

Pistons having oval cross sections transverse to the axes of thecylinders in which they reciprocate along at least a part of theirlengths are known. Conventionally, the major axis of the ellipse in thethrust and counterthrust face region of the skirt extends transverse tothe axis of the wrist pin. There are, for example, the pistonsillustrated and described in U.S. Pat. Nos.: 1,514,022; 2,262,132;2,309,555; 2,513,814; 4,470,375; and, 4,648,309.

Published Japanese Patent Specification 1-104,951 discloses a pistonhaving elliptical cross sections transverse to the piston and cylinderaxes in the crown and ring band region. The major axes of these ellipsesextend in the same direction as the axis of the wrist pin.

French Patent Specification 869,756 shows uniformly progressive ovalityof a piston. The piston has cross-sectional ovality at the bottom of itsskirt transverse to the piston pin axis, a progressive transitionthrough a circular cross section in the plane of the piston pin axistransverse to the cylinder axis, and a continuing uniform transition toovality in the opposite sense (that is, with the major axis of the ovalparallel to the piston pin axis) at the crown of the piston. This runscounter to modern piston design, wherein the designer strives tooptimize the competing considerations of heat transfer between the crownand cylinder wall on the one hand and clearance for reduced frictionalloss on the other hand.

Applicant makes no representation by this discussion, nor should anysuch representation be inferred, that an exhaustive search of allrelevant prior art has been conducted, or that no more pertinent priorart exists.

It is an object of the present invention to provide a piston designwhich reduces the so-called "dead volume" between the cylinder and thecrown and top land region. Reduction of this dead volume enhances fuelefficiency and reduces emissions.

According to the invention, a piston for an internal combustion enginehas a crown and top land region, an intermediate region including atleast one additional land, and a skirt region. Cross sections throughthe crown and top land region transverse to the cylinder axis are ovalswhose major axes are generally parallel to the axis of the piston pin.Cross sections through the intermediate region are either substantiallycircular or oval. Their longest dimensions are or equal to the length ofthe major axes of the ovals of the crown and top land region crosssections.

According to an illustrative embodiment of the invention, cross sectionsthrough the crown and top land region are uniform ovals.

Additionally, illustratively according to the invention, the longestdimensions of cross sections through the intermediate region are allsubstantially the same.

Further illustratively according to the invention, the longestdimensions of the cross sections through the intermediate region areless than the length of the minor axes of the ovals of the crown and topland region cross sections.

The piston further comprises a skirt region. The intermediate region islocated between the crown and top land region and the skirt region.According to an illustrative embodiment, cross sections through theskirt region transverse to the cylinder axis are ovals whose major axesare generally perpendicular to the piston pin axes.

Illustratively, the lengths of the major axes of the cross sectionsthrough the skirt region increase uniformly from the junction of theskirt region with the intermediate region to about the middle of thelength of the skirt region and then decrease from about the middle ofthe length of the skirt region to the remote end of the skirt region.

The invention may best be understood by referring to the followingdescription and accompanying drawings which illustrate the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a sectional side elevational view of a piston in acylinder in the plane defined by the cylinder's axis transverse to theaxis of the wrist pin;

FIG. 2 illustrates a sectional side elevational view of the piston andcylinder of FIG. 1 in the plane defined by the cylinder's axis and theaxis of the wrist pin;

FIG. 3 illustrates a sectional view taken along section lines 3--3 ofFIG. 1;

FIG. 4 illustrates a sectional view taken along section lines 4--4 ofFIG. 1; and

FIG. 5 illustrates a simplified sectional end elevational view of a fourstroke cycle, internal combustion engine, through a cylinder of theengine, containing a piston according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

A piston 10 is illustrated in FIGS. 1-5 in the cylinder 12 of an engine14. The piston rings have been omitted from the ring grooves for purposeof clarity. FIG. 1 illustrates a section through the piston 10 andcylinder 12. The plane of FIG. 1 is the plane defined by the axis 18 ofthe cylinder 12, and is transverse to the axis 20 of the wrist pin 22 bywhich the piston 10 is pivotally connected to a connecting rod 24. Theother end of the connecting rod 24, of course, is coupled to the engine14's crankshaft.

The plane of FIG. 2 is the plane defined by the axis 18 of the cylinder12 and the axis 20 of the wrist pin 22. FIGS. 3-4 illustrate somewhatfragmentarily views of the piston 10 in the cylinder 12 looking in thedirections of section arrows 3--3 and 4--4, respectively, in FIG. 1.Although the shape of the piston 10 in FIGS. 1-5 is exaggerated forpurposes of illustration, it will be appreciated that in the region ofthe crown 26 and top land 28 of piston 10, cross sections through thepiston 10 transverse to the cylinder 12's axis 18 are ovals, the longdimension, or major axis 30, of each of which extends generally parallelto the axis 20 of the wrist pin 22. These ovals illustratively aresymmetrical about the wrist pin axis 20. Illustratively, these ovals areellipses of uniform external (piston sidewall) dimensions. The purposeof this ovality of constant value (uniform oval cross section pistonouter wall) in the top land region 28 is to minimize so-called deadvolume between the top land 28's surface and the cylinder 12's wall.This dead volume receives the fuel air charge but does not effectivelyparticipate in the combustion "burn." Unburned gases scavenged from thisdead volume are exhausted primarily as unburned hydrocarbons. Theinvention thus lowers unburned hydrocarbon exhaust emissions.

It will further be appreciated that in the intermediate region 32extending from directly beneath the crown 26 and top land 28 to thebottom ring groove 37, cross sections through piston 10 transverse tothe axis 18 of the cylinder 12 can be either circular or oval, dependingupon the individual application. If these cross sections are ovals,their major axes will extend generally transverse to the piston pin axis20. The diameters of these circles or the lengths of the major axes ofthese ovals, as the case may be, are less than or equal to the lengthsof the major axes 30 of cross sections in the crown 26 and top land 28region. The intermediate region 32 includes the ring grooves 33, 35, 37,and the second and third lands 39, 41, respectively.

It will also be appreciated that in the region of the skirt 40 of piston10, cross sections through the piston 10 transverse to the cylinder 12'saxis are ovals, the long dimension, or major axis 42, of each of whichextends generally perpendicular to the axis 20 of the wrist pin 22.Generally, the lengths of major axes 42 are greater than the lengths ofmajor axes 30. The ovals in the skirt 40 region illustratively aresymmetrical about the wrist pin axis 20, with the piston 10's thrust andcounterthrust faces 46, 48 coming substantially more closely intocontact with the cylinder 12 wall toward the middle 49 of the length ofthe skirt 40. This configuration results in reduced slap during the highside thrust periods around bottom dead center and top dead center of thepiston 10's travel. Illustratively, the major axes 42 of the skirt 40'sovals increase from the skirt 40's junction with the intermediate region32 to the middle 49 of the skirt 40's length and then decrease uniformlyfrom the middle 49 of the skirt 40 toward its remote end 50. This makesthe skirt 40 somewhat barrel shaped in longitudinal section but oval, aspreviously described, in cross section.

I claim:
 1. A piston for connection by a piston pin and connecting rodto a crankshaft for reciprocating in a cylinder of a four-cycle internalcombustion engine, the piston having a crown and top land region, anintermediate region including at least one additional land, crosssections through the crown and top land region transverse to thecylinder axis being substantially uniform ovals, major axes of each ofthe ovals being generally parallel to a longitudinal axis of the pistonpin, cross sections through the intermediate region being one ofsubstantially circular and oval, major axes of each of the ovals of theintermediate region being generally transverse to the longitudinal axisof the piston pin.
 2. The piston of claim 1 wherein the cross sectionsthrough the crown and top land region are uniform ovals.
 3. The pistonof claim 1 or 2 wherein longest dimensions of cross sections through theintermediate region are all substantially the same.
 4. The piston ofclaim 3 wherein longest dimensions of the cross sections through theintermediate region are less than lengths of minor axes of the ovals ofthe crown and top land region cross sections.
 5. The piston of claim 4and further comprising a skirt region, the intermediate region locatedbetween the crown and top land region and the skirt region, crosssections through the skirt region transverse to the cylinder axis beingovals with major axes of the ovals being generally perpendicular to thelongitudinal axis of the piston pin.
 6. The piston of claim 5 whereinlengths of the major axes of the cross sections through the skirt regionincrease uniformly from a junction of the skirt region with theintermediate region to about mid-length of the skirt region and thendecrease from about mid-length of the skirt region to a remote end ofthe skirt region.
 7. The piston of claim 3 and further comprising askirt region, the intermediate region located between the crown and topland region and the skirt region, cross sections through the skirtregion transverse to the cylinder axis being ovals with major axes ofthe ovals being generally perpendicular to the longitudinal axis of thepiston pin.
 8. The piston of claim 7 wherein lengths of the major axesof the cross sections through the skirt region increase uniformly from ajunction of the skirt region with the intermediate region to aboutmid-length of the skirt region and then decrease from about mid-lengthof the skirt region to a remote end of the skirt region.
 9. The pistonof claim 1 or 2 wherein longest dimensions of cross sections through theintermediate region are all less than lengths of minor axes of the ovalsof the crown and top land region cross sections.
 10. The piston of claim9 and further comprising a skirt region, the intermediate region locatedbetween the crown and top land region and the skirt region, crosssections through the skirt region transverse to the cylinder axis beingovals with major axes of the ovals being generally perpendicular to thelongitudinal axis of the piston pin.
 11. The piston of claim 10 whereinlengths of the major axes of the cross sections through the skirt regionincrease uniformly from a junction of the skirt region with theintermediate region to about mid-length of the skirt region and thendecrease from about mid-length of the skirt region to a remote end ofthe skirt region.
 12. The piston of claim 1 or 2 and further comprisinga skirt region, the intermediate region located between the crown andtop land region and the skirt region, cross sections through the skirtregion transverse to the cylinder axis being ovals with major axes ofthe ovals being generally perpendicular to the longitudinal axis of thepiston pin.
 13. The piston of claim 12 wherein lengths of the major axesof the cross sections through the skirt region increase uniformly from ajunction of the skirt region with the intermediate region to aboutmid-length of the skirt region and then decrease from about mid-lengthof the skirt region to a remote end of the skirt region.